1. Field of the Invention
The present invention relates to an ink jet recording head for performing a recording operation by discharging ink, a substrate for such a head, a method of manufacturing such a substrate, and an ink jet recording apparatus.
2. Related Background Art
In an ink jet recording system of the type disclosed in U.S. Pat. Nos. 4,723,129 and 4,740,796, for example, a recording operation can be performed at a high speed with high density, high accuracy, and high image quality. Such a system also provides suitable coloring and compactness. An ink jet recording system typically operates by discharging ink onto a recording medium by utilizing thermal energy to bubble the ink. A recording head for such a system generally is constructed by providing a heating resistor, for generating a bubble in the ink, and wiring, for providing an electrical connection to the heating resistor, on a substrate. A nozzle for discharging the ink generally is also formed on this substrate. resistor. Typically, the protective film has a thickness of about 1 xcexcm.
Japanese Laid-Open Patent Application No. 08-112902 describes a method for partially reducing the thickness of the protective film on the heating resistor while stabilizing its protective function with respect to the wiring. With this method, the amount of energy applied can be reduced and the life of the recording head can be stabilized by reducing the thickness of the protective film only on the heating resistor.
In the above example, a heating resistor and a wiring pattern are first formed on a silicon oxide film on a substrate. Next, silicon oxide is formed as a first protective film layer. Next, the first protective film layer is partially removed from a heating portion of the heating resistor by patterning. Finally, silicon nitride is formed as a second protective film layer. This arrangement, however, has the following problems.
The first protective film layer normally is partially removed from the heating portion by wet etching. If the first protective film layer is formed of silicon oxide, a hydrogen fluoride-based etching liquid is used. The heating resistor, which is generally constructed of HfB2 and TaN, is not damaged by the hydrogen fluoride-based etching liquid.
Here, there is no problem in a manufacturing process when the removed portion of the protective film is inside the heating portion of the heating resistor
The substrate for the ink jet recording head includes various means for saving applied electric energy, on the one hand, and for preventing a reduction in the life of the substrate resulting from mechanical damage caused by the bubbling of the ink and the destruction of a heating portion caused by a thermal pulse, on the other hand. In particular, the substrate has a protective film for protecting the heating resistor, and, specifically, a heating portion located between a pair of wiring patterns, from the ink.
To maximize thermal efficiency, it is advantageous that this protective film have a high thermal conductivity or be relatively thin. However, to minimize mechanical damage and the probability of a defect in the protective film caused by the bubbling of the ink, it is advantageous that the protective film be relatively thick. Further, the protective film also protects the wiring connected to the heating resistor from the ink, which requires that the protective film have a certain thickness.
The surface of the heating resistor is generally very smooth and the protective film can be closely formed on this surface. In contrast, the wiring is generally formed from aluminum (Al), the surface of which tends to be influenced by heat during the manufacturing process, and, therefore, often has irregularities. Further, the aluminum is about 500 nm thick, so that the quality of the protective film is degraded where the wiring steps down to the heating by about several xcexcm. However, thermal efficiency is reduced since the removed portion is a relatively small area within the heating portion as compared to the total area of the heating portion.
In contrast, when the first protective film layer is formed with a step difference between the wiring and the heating resistor and the substrate below the heating resistor, the quality of the first protective film layer oftentimes is poor in this step difference portion. Therefore, when the first protective film layer is widely removed over the heating portion of the heating resistor, a portion of the protective film near the step difference between the heating resistor and the substrate below the heating resistor is etched. Accordingly, undercut is advanced along the step difference portion, which has a relatively poor film quality, so that an air hole is caused in the film interior. As a result, the life of the recording head substrate is reduced. The quality of the first protective film layer in the step difference portion is further degraded since a vertical etching technique is often employed to provide a fine structure and since a cross section of the heating resistor rises steeply at approximately 90xc2x0. Accordingly, it has been necessary to strictly control the etching time of the first protective film layer to reduce the undercut as much as possible.
An object of the present invention is to provide an ink jet recording head, a substrate for such a head, a method of manufacturing such a substrate, and an ink jet recording apparatus for solving the above problems by utilizing as much of a heating portion of a heating resistor as possible through an easily controlled process. Thus, the present invention lengthens the life of the recording head while saving energy by improving thermal efficiency.
Another object of the present invention is to provide an ink jet recording head, in which a heating resistor forming a heating portion, wiring electrically connected to the heating resistor, and a protective film formed on the heating resistor and the wiring to protect the heating resistor and the wiring are arranged on a substrate for the ink jet recording head. An ink path, in communication with a discharging port for discharging ink, also is formed on the substrate for the ink jet recording head. The protective film includes a first protective film layer for covering the heating resistor and the wiring, a second protective film layer formed on the first protective film layer of a material different from that of the first protective film layer and having an opening in a portion corresponding to the heating portion of the heating resistor, and a third protective film layer constructed of the same material system as the first protective film layer and covering the second protective film layer and the portion of the first protective film layer that is exposed through the opening. The second protective film layer is constructed of an inorganic material.
Another object of the present invention is to provide a substrate for an ink jet recording head, in which a heating resistor forming a heating portion, wiring electrically connected to the heating resistor, and a protective film formed on the heating resistor and the wiring to protect the heating resistor and the wiring are arranged on the substrate. The protective film includes a first protective film layer for covering the heating resistor and the wiring, a second protective film layer formed on the first protective film layer of a material different from that of the first protective film layer and having an opening in a portion corresponding to the heating portion of the heating resistor, and a third protective film layer constructed of the same material system as the first protective film layer and covering the second protective film layer and the portion of the first protective film layer that is exposed through the opening. The second protective film layer is constructed of an inorganic material.
Still another object of the present invention is to provide a method of manufacturing a substrate for an ink jet recording head, in which a heating resistor forming a heating portion, wiring electrically connected to the heating resistor, and a protective film formed on the heating resistor and the wiring to protect the heating resistor and the wiring are arranged on the substrate. The method comprises the steps of forming a first protective film layer so as to cover the heating resistor and the wiring, forming a film of an inorganic material that is different from the material of the first protective film layer on the first protective film layer, etching the film of inorganic material in a portion corresponding to the heating portion of the heating resistor and removing the inorganic material film from this corresponding portion to form a second protective film layer having an opening in the corresponding portion, and forming a third protective film layer of the same material system as the first protective film layer so as to cover the second protective film layer and the portion of the first protective film layer that is exposed through the opening.
In the present invention, since the heating resistor and the wiring are covered with the first protective film layer, the step difference is lessened in corner portions of the heating resistor and the wiring pattern. Accordingly, the quality of the second protective film layer formed on the first protective film layer is improved and overetching is substantially avoided along the step difference portion when the second protective film layer is etched.
The third protective film layer, which is constructed of the same material system as the first protective film layer, serves as a protective film for the heating portion, together with the first protective film layer left on the heating portion. Further, the third protective film layer is laminated with the first and second protective film layers thereon so that a protective film having at least three layers is formed on the wiring. Thus, the films are formed by dividing these films into plural layers. Accordingly, when there is a defect in any one portion of a protective film of one layer, it is possible to reduce the probability of an occurrence of a defect caused in a portion of the entire protective film of a plural-layer structure.
Thus, in accordance with the present invention, it is possible to provide an ink jet recording head, a substrate for such a head, a method of manufacturing such a substrate, and an ink jet recording apparatus, with energy savings, stable lifetimes, and convenient process control.